JPS5950002B2 - Steam temperature control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a steam temperature control device for controlling steam temperature on the outlet side of a boiler superheater.

Conventionally, in order to control the steam temperature at the outlet side of a boiler superheater to a predetermined value, the deviation between the steam temperature set value and the detected value is calculated,
In order to reduce this deviation to zero, the spray amount is determined by a PID (proportional-integral-derivative action) controller and the spray type desuperheater is operated to control the steam temperature.

FIG. 1 shows such a conventional steam temperature control device.

That is, as shown in FIG.
A comparator 3 compares the detected steam temperature value S8 with a steam temperature set value So to calculate the deviation, which is then added to the PID controller 4.

This PID controller 4 has a steam temperature set value S.

The spray amount is determined so as to make the deviation of the detected value Sa zero, and the spray system 5 is activated by a signal corresponding to this spray amount.
control the valve 6 provided in the

By controlling this valve 6, the steam system 1 on the inlet side of the superheater 2
Spray water SP is supplied to a spray-type desuperheater 7 provided in the steam tank to control the steam temperature.

However, in such a steam temperature control device, the superheater 2
When the steam temperature on the outlet side changes due to a change in the steam temperature on the inlet side of A value S8 is added.

Therefore, even if the spray amount is determined as described above using this steam temperature detection value Sa and the spray type desuperheater 7 is operated, effective control cannot be achieved.

Therefore, recently, in order to perform more effective control, the following control method has been adopted as a steam temperature control device.

First, in the first method, in addition to the above-mentioned components in FIG. 1, a temperature detection terminal is provided on the upstream side of the desuperheater 7 as shown by the dotted line to detect the steam temperature before spraying, and this detected value Sb is added to the coefficient unit 8 and multiplied by a predetermined coefficient, and this is added together with the output of the PID controller 4 by the adder 9, and the added output controls the valve 6 to manipulate the spray amount in a feedforward manner. This is what I did.

However, even if this first method is adopted, if the steam flow rate changes due to changes in the boiler load, the steam temperature will change.

In addition to the components of the first method described above in FIG. 1, the second method also includes a steam flow rate detector 10 in the steam system 1 on the outlet side of the superheater 2 as shown by the dashed line in the figure. The signal Sc corresponding to
In addition, this coefficient unit or function generator 11 calculates the spray amount corresponding to the steam flow rate determined from the steady-state characteristics to obtain an output, and this output is combined with the output of the PID controller 4 and the coefficient unit 8.
is added together with the output of , by an adder 9, and the added output is used to control the valve 6 to manipulate the spray amount.

In this case, the steam temperature changes not only when the steam flow rate changes but also when the boiler heat input changes.

Therefore, if the boiler heat input is changed in equilibrium with the steam amount,
This variation no longer appears noticeably.

However, when the boiler heat input is changed in equilibrium with the steam amount and the steam flow rate is changed by changing the load demand, the steam pressure immediately changes.

Therefore, in order to compensate for this pressure fluctuation, the boiler heat input amount can be manipulated by also using the differential signal of the steam flow rate change.

However, even if the measures according to the second method are taken, an imbalance will occur between the amount of steam and the amount of heat input to the boiler during a transient period of change in load demand, causing the steam temperature to fluctuate.

Furthermore, the third method overcomes the shortcomings of the second method, so
A spray amount proportional to the unbalanced amount of boiler heat input and steam amount is calculated, and this is added to the adder 9 shown in Fig. 1, and the added output controls the valve 6 to manipulate the spray amount. This is what I did.

Therefore, in this third method, if the dynamic characteristics brought about by the unbalanced amount of boiler heat input and steam amount in the fluctuation of steam temperature and the dynamic characteristics of the change in steam temperature due to the change in the amount of spray, then the steam due to the unbalanced Can compensate for temperature fluctuations.

However, in general, the dynamic characteristics of the two are different, and even if the deviation in steam temperature due to unbalance can be reduced to zero in a steady state, the steam temperature fluctuates in a transient state due to the difference in dynamic characteristics.

Therefore, although this third method is effective when there is a steady imbalance between the amount of steam and the amount of heat input to the boiler,
This method is not very effective as a method for compensating for steam temperature fluctuations due to unbalance caused by changes in load demand.

The present invention has been made in view of the above-mentioned circumstances, and is designed to effectively manipulate the spray amount so as not to cause fluctuations in steam temperature caused by imbalance between the steam flow rate and boiler heat input that occurs transiently when changing the steam flow rate. The purpose of the present invention is to provide a steam temperature control device that can control the temperature of steam.

In explaining one embodiment of the present invention with reference to the drawings below, the concepts of boiler heat input and steam amount will be described first.

A boiler is a device whose purpose is to burn fuel such as heavy oil, flammable gas, or coal, evaporate water, and generate steam.It generates steam in an amount, temperature, and pressure commensurate with the amount of heat supplied to the boiler. do.

That is, as the amount of heat supplied increases, the amount of steam generated increases, and the temperature and pressure rise.

Conversely, if the amount of heat supplied is reduced, the amount of steam generated will be reduced, and the temperature and pressure will be lowered.

Note that the boiler heat input means the amount of heat supplied to the boiler, and this amount is proportional to the fuel flow rate, and can be represented by a detected value of the fuel flow rate measured with a flowmeter or a command value.

The steam generated in the boiler is led to a steam turbine and used for power generation, or for various purposes within the factory.

Therefore, the boiler is required to generate steam according to the electric power demand and the amount of steam demanded in the factory, and the amount of steam is the output of the boiler and also the amount of load imposed on the boiler.

Furthermore, the amount of steam coming out of the boiler can be adjusted by opening and closing steam valves provided in the steam pipes.

Therefore, the amount of steam can be represented by the load requirement, the opening of the steam valve, or the detected value of the steam flow rate measured by a flow meter.

FIG. 2 shows the configuration of the steam temperature controller 12, which is the main part of the present invention. It consists of a transfer characteristic element 14 for dynamic characteristic compensation to which a subtraction element 13 and an output S obtained from the subtraction element 13 are added, and the output Sg of this transfer characteristic element 14 is added to the adder 9 shown in FIG. be.

Here we will discuss the functions of each element.

The subtraction element 13 with a function element receives a signal Sd corresponding to the boiler heat input amount such as a combustion command value or a detected fuel flow rate value, and a signal Se corresponding to the steam amount such as a load request amount, a steam valve opening degree, or a detected steam flow rate value. When received, the amount of unbalance between the two is calculated and transmitted as a difference signal Sf.

The dynamic characteristic compensation transfer characteristic element 14 converts the characteristics of this difference signal Sf and transmits a spray amount signal S.

This spray amount signal Sg is added by an adder 9 together with the spray amount signal determined by the conventional controller shown in FIG. 1 to form the actual spray operation amount.

By the way, the subtraction element 13 with a function element calculates the boiler adult heat amount that is balanced with the input steam flow rate at that time using a function generation element, subtracts this value from the manually input boiler heat input amount, and transmits a difference signal.

In addition, the function generator calculates the amount of steam that is in equilibrium with the input boiler heat input at that time, and sends a signal that subtracts the input steam amount from this value.

Note that if the boiler heat input balanced with the steam amount is in a proportional relationship, the functional element may be a coefficient element that is multiplied by a predetermined ratio coefficient.

The transfer characteristic element 14 for dynamic characteristic compensation is a transfer characteristic G of steam temperature caused by an imbalance between the steam amount and the boiler heat input.
, (S) and (S nira plus operator), which compensates for the difference in the characteristics of the transfer characteristic G2 (S) of the steam temperature change caused by the change in the spray amount, and is an element with a transfer characteristic expressed as a transfer function. be.

Note that if the characteristics of G(S) are complex, elements with simplified approximate characteristics may be used.

Furthermore, if the differential effect is strong, an element with approximate characteristics with weaker differential characteristics may be used.

In this case, although it is not possible to completely compensate for fluctuations in steam temperature due to imbalance between the boiler heat input and the amount of steam, it is possible to suppress fluctuations to a greater extent than in the case where dynamic characteristic compensation is not performed.

Next, the operation of the present invention will be explained using a specific example.

The transfer characteristic to steam temperature due to the imbalance between boiler heat input and steam amount is given by equation (2).

That is, it is a first-order lag characteristic with a lag time constant of 2/2.

Also, the process gain of 1/40 is when the unbalance amount between the boiler heat input and the steam amount is 40 kl/sec in terms of fuel flow rate.
This means that the steam temperature changes by 1°C.

Here, the above equation (2) was obtained by investigating the characteristics of the boiler in which the present invention was implemented, and when only the boiler heat input was changed stepwise in an equilibrium state, the response as shown in Figure 3a was obtained. was gotten.

The process gain is 1/40 from the ratio of the step input amount to the final value of this response diagram, and the delay time is 2 from the time from adding the step input to reaching 63.2% of the final value in this response diagram. Equation (2) was obtained by finding the minutes.

In addition, the transfer characteristics to steam temperature due to changes in spray amount are (
3) Given by Eq.

Here, the above equation (3) was obtained by investigating the characteristics of the boiler in the same manner as described above, and when the spray amount was varied in a stepwise manner, a response as shown in FIG. 3 was obtained.

Therefore, from this figure, as described above, (3) formula % formula % That is, it is a third-order lag characteristic with a lag time constant of 1 minute.

In addition, the process gain -5 changes the spray amount to Q, 2t
/hr means that the steam temperature changes by 11°C.

Figure 31] shows how the steam temperature changes when the spray amount is increased in steps of Q, 2t/hr.

Therefore, the steam temperature controller 1 applied to this process
Transfer characteristic G (S) of dynamic characteristic compensation transfer characteristic element 14 of 2
becomes equation (1) to equation (4).

Here, when the unbalance occurs in a step shape by 40 kl/hf in terms of fuel quantity, the dynamic characteristics of the steam temperature fluctuation are (2
) gives the following equation, and this fluctuation waveform is shown in FIG. 3a.

That is, if no control is performed, the steam temperature will be disturbed in this waveform, and a steady deviation of 1° C. will occur.

In order to compensate for this fluctuation, the spray amount is increased in steps of 0.2 t/h at the same time as the imbalance occurs, and the change in steam temperature is calculated by adding the waveforms in Figures 3a and 3d.
The shape is shown in Figure C, and if expressed in equations, it becomes equation (6) from equation (5) and equation (3).

In other words, although the steady-state deviation becomes zero, it is not possible to compensate for transient fluctuations, and as the amount of imbalance increases, the peak of the fluctuation increases in proportion to it.

However, if the steam temperature controller 12 described above is used, when a difference signal (unbalanced amount) of 40 kl/hr in terms of fuel amount is generated, a spray amount having the characteristics of the following equation is transmitted, and from equation (4) to (7) ).

The steam temperature change characteristics brought about by this spray amount signal are:
The following equation is obtained from equations (3) and (7).

This is the equation (5) with its sign reversed, and when equations (5) and (8) are added, it becomes zero.

That is, it is possible to completely cancel out the temperature fluctuations caused by the imbalance between the amount of steam and the amount of heat input to the boiler, and to make the temperature fluctuations zero even during transient times.

The state at this time is shown in FIG. 3C.

Next, a case will be described in which an approximate characteristic, for example, an element having the characteristic of equation (9) is used as the dynamic characteristic compensation transfer element 14.

Similarly to the above, when an imbalance of 40kl/hr occurs,
The manipulated variable transmitted by this controller is expressed by the following equation from equation (9).

The influence of this on the steam temperature is expressed by the following equation from equations (3) and (10).

Therefore, the fluctuation characteristics of the steam temperature under control using this controller when unbalance occurs are formed by equations (5) and (M).

In this case, although the fluctuation cannot be completely compensated for, the peak value of the fluctuation waveform shown in FIG. 3C without dynamic characteristic compensation can be kept low.

Note that if a minor control loop is provided to control the outlet steam temperature of the spray type desuperheater 7, the output of the adder 9 will temporarily change the target value of this minor control loop and indirectly control the spray amount. operate.

In this case, the transfer characteristic G (S
) used to determine G2(S) may be a change characteristic of the superheater outlet steam temperature a with respect to a change in the output of the adder 9, which is an approximate spray amount signal.

Therefore, in the boiler steam temperature control system shown in FIG.
When the steam flow rate is changed by the load request command, the steam pressure fluctuates.

In order to quickly recover from this fluctuation, the boiler heat input amount is changed using also the differential signal of the change in steam flow rate.

Therefore, in a transient state, the balance between the boiler heat input and the steam amount is disrupted, causing fluctuations in the steam temperature.

In other words, if we focus on steam pressure, the controllability of steam pressure can be improved by rapidly changing the boiler heat input during transitions of changes in steam volume and intentionally making the steam volume and boiler heat input unbalanced. However, the steam temperature fluctuates widely.

Conversely, if we focus on the steam temperature, we can improve the controllability of the steam temperature by changing the boiler heat input without balancing it with the steam volume; It takes time.

For this reason, in the conventional system, the control parameters of the controller had to be adjusted to a compromise between steam pressure fluctuation and steam temperature fluctuation.

However, in the present invention, by using the steam temperature controller 12 as shown in FIG. 2 and adding its output Sg to the adder 9 of the control system shown in FIG. It is possible to compensate for fluctuations in steam temperature caused by an imbalance between the amount of steam and the amount of heat input to the boiler.

Therefore, there is no need to find a compromise in steam pressure control while taking into account fluctuations in steam temperature, and it is possible to freely manipulate the boiler heat input by considering only the controllability of steam pressure.

As a result, when changing the amount of steam, it is possible to effectively control the fluctuations that occur in both steam temperature and steam pressure at the same time, and boiler plans 1 to 2 have good ability to follow sudden changes in power demand. It becomes possible to do so.

As described above, according to the present invention, it is possible to effectively control the operation of the spray amount so as not to cause fluctuations in the steam temperature caused by the imbalance between the steam flow rate and the boiler heat input that occurs transiently when changing the steam flow rate. We can provide a steam temperature control device that can.

[Brief explanation of drawings]

FIG. 1 is a system diagram for explaining a conventional steam temperature control device, FIG. 2 is a configuration diagram of a steam temperature controller according to an embodiment of the present invention, and FIG. 3 is a system diagram for explaining a conventional steam temperature controller. FIG. 3 is a waveform diagram for explaining steam temperature fluctuations. 1... Steam system, 2... Superheater, 3... Comparator, 4
...PID controller, 5...Spray system, 6...Valve, 7...Spray type superheat reducer, 8...Coefficient unit, 9...Adder, 10...Steam flow rate Detector, 11.
... Coefficient unit or function generator, 12 ... Steam temperature controller, 13 ... Subtraction element with function element, 14 ... Dynamic characteristic compensation transfer characteristic element.

Claims (1)

[Claims] 1. In a boiler steam system equipped with a superheater and a spray type heat reducer on the inlet side of the superheater, the steam temperature and steam amount on the outlet side of the superheater and the steam temperature on the inlet side of the spray type superheat reducer, respectively. In the steam temperature control device, the spray amount is determined by detection and calculation, and the spray type desuperheater is operated based on the spray amount to control the steam temperature on the outlet side of the superheater to a predetermined value. A subtraction element with a function element that inputs a signal corresponding to the heat input amount and a signal corresponding to the steam amount and calculates the amount of unbalance between the two, and a difference signal output from this subtraction element is input to calculate the boiler heat input amount and the steam amount. a transfer characteristic element for dynamic characteristic compensation that transmits the spray amount and has a transfer characteristic that compensates for the difference between the transfer characteristic to the steam temperature fluctuation due to the unbalanced amount and the transfer characteristic to the steam temperature change due to the change in the spray amount; A steam temperature control device comprising an addition element that adds the output of the transfer characteristic element for dynamic characteristic compensation to the spray amount calculated from the steam temperature on the outlet side of the superheater.